1. Field of the Invention. This invention relates to improvements in die-up ball grid array BGA packages for integrated circuits.
2. Prior Art. FIG. 1 illustrates a conventional die-up fine pitch ball grid array FPBGA package 50 in which an integrated-circuit die 52 is adhesively mounted to a top surface of a flexible, insulated polyimide tape 54. Bonding wires 56 are connected between wire-bonding pads on a top surface of the integrated-circuit die 52 and wire-bonding sites 58 on the top surface of the insulated polyimide tape layer 54. The integrated-circuit die, the bonding wires, and the conductive bonding sites on the top side of the insulated tape layer are all encapsulated in an encapsulation cap 60.
Conductive traces are formed on the top surface of the insulated polyimide tape. The conductive traces provide connections between the wire-bonding sites 58 and a number of solder-ball mounting areas, typically shown as 62, which are also formed on the top side of the insulated polyimide tape. A number of holes, typically shown as 64, are formed through the insulated polyimide tape layer to expose the bottom sides of the solder-ball mounting areas 62 on the top side of the insulated polyimide tape. The holes allow solder balls, typically shown as 66, to be attached through the holes in the insulated polyimide tape to the solder-ball mounting areas on the top side of the insulated polyimide tape.
The solder-ball mounting areas are arranged in a grid pattern. In order to mount an HBGA package to the surface of a printed-circuit board, the grid pattern of the solder balls is placed over a corresponding grid pattern of solderable areas on the printed-circuit board. The solder balls are then heated to a temperature sufficient to melt the solder balls and to solder the BGA package to the surface of the printed-circuit board.
The insulated polyimide tape layer of a conventional die-up BGA package is good for routing of conductive traces but is limited when solder ball pads are to be attached to the tapes because the conductive traces have to go around the solder ball pads which interfere with routing of the conductive traces on the insulated tape layer. A problem with a conventional die-up BGA package, which uses an insulated polyimide tape layer, is that, particularly for large body sizes, warpage can occur due to the thinness and softness of the tape.